In the field of flat-panel-type display apparatuses, typical of which are liquid-crystal display apparatuses and EL (electroluminescence) display apparatuses, so-called driving-circuit-united-type display apparatuses have been developed in order to make the frames of the panels smaller and make the panels thinner. In the driving-circuit-united-type display apparatuses, a display section in which pixels are arranged in a matrix manner and peripheral driving circuits for driving the display section are mounted on a transparent, insulating substrate as a unit. In liquid-crystal display apparatuses and EL display apparatuses, since thin-film transistors (TFT) are used as pixel transistors, the peripheral driving circuits are also formed by using TFTs when the peripheral driving circuits are mounted on a transparent, insulating substrate.
The peripheral driving circuits of the display apparatuses include a vertical driving circuit for selecting pixels in the display section in units of lines and a horizontal driving circuit for writing display data into each pixel in the selected line. In addition, a data processing circuit for applying various processes to display data to be sent to the horizontal driving circuit needs to be included. It is assumed here that the data processing circuit is formed by using TFTs on a transparent, insulating substrate, such as a glass substrate, in a display apparatus.
TFTs have much variance in element characteristics and the absolute values of their thresholds Vth are large. When TFTs are formed on an insulating substrate, such as a glass substrate, it is known that their element characteristics become worse than when TFTs are formed on a silicon substrate. Therefore, when a data processing circuit is formed on an insulating substrate by using TFTs, where the absolute values of the thresholds Vth are large, it is difficult to process at a high speed, data signals having high data rates, such as digital display data signals.
Even when the absolute values of the thresholds Vth are large, if the power-supply voltage of the circuit is set high and the data signals are handled as large-amplitude signals, it is possible to handle digital data signals having high data rates at a high speed. When the power-supply voltage of the data processing circuit is set high, however, the power consumption of the data processing circuit increases very much. Therefore, it is disadvantageous when the display apparatus has a driving-circuit-united-type structure to reduce its power consumption.
The present invention has been made in consideration of the above issues. An object of the present invention is to provide a data processing circuit capable of processing digital data signals at a high speed with a low power consumption even if the data processing circuit is formed on an insulating substrate by using TFTs, a display apparatus which uses the data processing circuit as one of peripheral driving circuits for a display section, and a portable terminal in which the display apparatus is mounted as an image display section.